An encoding transmission/reception technology is adopted in an ultrasonographic method and ultrasonographic device in order to enhance a resolution of an ultrasonograph. A complementary encoding technology typically such as Golay (Golay, M. J. E. Complementary Series. IRE Trans. Inform. Theory, IT-7, pp. 82-87, April 1961) is known as the encoded exchange technology. According to the technology, an encoding set including two complementary modulation codes (A and B) is available, and a basic wave is modulated by the modulation codes (A and B) in the encoding set and is output to a probe as encoding drive signal so that an encoded ultrasonic beam can be transmitted from the probe to a subject. The two received signals corresponding to the ultrasonic beam are demodulated and synthesized so that the time side lobe due to code demodulating processing can be reduced.
The time side lobe may occur due to nonlinearlity of a medium within a subject. Accordingly, an opposite polarity encoding set is created including two modulation codes having inverted polarities (such as −A and −B) of the two modulation codes (A and B) of an encoding set, and an ultrasonic beam is transmitted based on each of the modulation codes (−A and −B) of the opposite polarity encoding set and each of the modulation codes (A and B) of the encoding set. Then, the reception signal corresponding to the encoding set and the reception signal corresponding to the opposite polarity encoding set are synthesized so that the time side lobe due to nonlinearity of the medium within the subject can be reduced (as in Japanese Unexamined Patent Publication No. 7-59766).
However, while the time side lobe may occur due to nonlinearlity of a medium within a subject and/or a body motion (such as a change in position or form with time), the conventional technology does not consider reducing the time side lobe due to a body motion of a subject.
It is an object of the invention to reduce the time side lobe due to a body motion of a subject.